They were all for movement where, another slave state that didn't want them or to a Northern or western state that didn't want them? In any case, the law wasn't strongly enforced in the South, Maryland and Virginia had the largest population of free blacks in the country, North Carolina was in the top five or six and all Southern Sates had free blacks with long time residency.
The issue, of course, from free blacks' point of view is exactly what you mentioned: southern states wanted free blacks out because they could stir up trouble and jealousy among slaves, but free blacks couldn't just randomly go anywhere in the north and be accepted either. The southern states didn't care, of course--they just wanted them gone. I'm tracing members of an extended free black family who left Virginia (voluntarily; they had been born free) and they tended to wind up in areas that were abolitionist strongholds, probably for that very reason.
My main goal is to understand history overall, rather than to debate in a way that makes one side look better to modern sensibilities. Such debate is useful too, because it brings up instructive points, but the problem comes when information is presented selectively. Those who are aware of the wider context see the rhetorical distortion, but those who aren't think it's the whole truth.
A couple of points: Enforcement of
both northern and southern free-black laws came and went in cycles. There would be a race riot in the north or an insurrection in the south, people would wring their hands and demand something be done, politicians and law-enforcement officials would comply and crack down hard, then would slack off again. Think school shootings or 9/11--it's still the way things work today. So saying that the law wasn't strongly enforced in the south is just as true, or untrue, for the north. Sometimes it was, sometimes it wasn't.
Also, the size of the free black population is irrelevant, because most of the increase was due to children who were born free or people who were manumitted before the laws requiring moving away. As I noted, the southern laws requiring free blacks to leave only affected
newly-freed blacks, not those who had been born free in the state, though there were
a few exceptions where slave states tried to remove all free blacks, even those who had been born there. They usually lasted only briefly or didn't work out well.
However, free blacks who were born in slave states still had to jump through hoops to stay there, similar to the laws in northern states, such as register and pay an annual fee. They faced one danger in slave states that they didn't in free ones--the possibility of being sold into slavery for not complying with the law. In free states, the worst that could happen was being expelled to another state or imprisoned.
Though free blacks were a small percentage of all blacks in the south, especially the rural south, they're still a worthwhile group to study. But I hate to see their stories used merely to score debating points in modern arguments about how good or bad northern or southern whites used to be, rather than as stories about people in their own right.